In the description below, the term “automatic gearbox” should be taken in the broad sense, as it can cover all kinds of gearboxes, notably robotized gearboxes with single or double clutch.
It should be borne in mind that this type of box can operate either in automatic mode, with the gears being changed automatically at an appropriate moment, or in manual mode, with the gears being changed by the driver via buttons, levers, etc. In automatic mode, the lever or other control systems can generally have different positions, namely a P (Park) position, R (Reverse) position, N (Neutral) position, D (Drive) position and, possibly, S (Sport) position.
Regardless of the type of automatic gearbox, the latter must incorporate a locking system when the vehicle is in (P) position. Generally, this locking system is implemented by a rod able to interoperate with a toothed wheel built-into part of the gearbox. This rod can be operated by a carriage that has, at one end, superimposed rollers, of which one interoperates with a cam profile on the rod that can interoperate with a toothed wheel built into a part of the gearbox. The other end of the carriage is coupled to a rod mounted in association with a spring that can be controlled by a linear sideways movement. The purpose of this rod is to take-up the non-movement that can result, in the P position of the gearbox control device, from non-engagement of the finger into a notch in the toothed wheel. This linear slide system—which can absorb, or not absorb, this difference in movement resulting from the positioning of the finger in relation to a notch (gearbox locking) or not (non-locking of the gearbox)—is fairly bulky.